The present invention relates to a lithographic printing plate in which aluminum or an aluminum alloy is used as a support, and a method for producing the same. In particular, the present invention relates to a lithographic printing plate complying with automated accumulation, exposure and development procedures thereof, and a method for producing the same.
The present invention further relates to a method for producing a support for a lithographic printing plate, and particularly to a method for producing a support for a lithographic printing using aluminum or an aluminum alloy.
In recent years, with the progress of automated platemaking in lithographic printing, lithographic-printing plates more excellent in flatness, as well as lithographic printing plates having better printing performance, have been required in order to make it possible to cut and accumulate them more stably and at higher speed, complying with automated platemaking and mass production.
The flatness is disclosed in JP-A-8-104069 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d). The above-mentioned patent proposes a material specified in tensile strength and warping in a rolling direction in a coil-like raw plate of an aluminum alloy plate after final cold rolling, and describes that the coil-like aluminum raw plate having flatness so as not to induce exposure deviation of a lithographic plate can be supplied thereby even in an automatic conveying step of a lithographic photosensitive printer.
In the technique disclosed in the above-mentioned patent, the printer using the support for the lithographic printing plate is stably automated by specifying the characteristics of the raw material. However, particularly in recent years, it is necessary to improve the flatness of the lithographic printing plates for increased efficiency of exposure and development, as well as further improvement in printing performance of the lithographic printing plates, and also in terms of cost, further improvement in productivity of the lithographic printing plates has been earnestly desired. Accordingly, even the technique disclosed in the above-mentioned patent is not said to be sufficient yet.
On the other hand, aluminum and aluminum alloys are used as aluminum supports for printing plates, particularly supports for lithographic printing plates.
In general, in order to use aluminum plates as substrates for lithographic printing plates, it is necessary that they have appropriate adhesion to photosensitive agents and water receptivity, and that surfaces thereof are uniformly roughened. The uniformly roughened surfaces require that the size of pits formed is appropriately uniform and such pits are uniformly formed on the whole surfaces. The pits significantly influence the scumming reduction and the printing durability, the printing performances of plate materials, and good or bad thereof is an important factor in the production of the plate materials.
JP-A-6-92052 proposes an invention comprising the steps of mechanically roughening a surface, followed by etching within the range of 0.5 to 30 g/m2, and performing pulse energizing of 200 to 600 c/dm2. Further, JP-A-7-9776 proposes to conduct etching in 1 to 5 g/m2 after mechanical surface roughening, and performing electrochemical surface roughening at an alternating current quantity of electricity of 300 to 800 c/dm2. JP-A-6-24166 proposes an invention comprising the steps of mechanically roughening a surface, followed by etching within the range of 0.5 to 30 g/m2, and conducting alternating current electrolysis at 200 to 600 c/dm2. Methods for roughening surfaces of substrates include mechanical surface roughening, chemical etching and electrochemical surface roughening. In JP-A-6-24166, an invention is also disclosed in which various conditions of mechanical surface roughening, chemical etching and electrochemical surface roughening are changed. That is, it proposes that a surface is chemically etched in 0.5 to 30 g/m2 after mechanical surface roughening, electrochemically roughened by giving an appropriate current density and quantity of electricity, then, etched within the range of 0.1 to 10 g/m2 to smooth edges, and subjected to anodization.
In addition, U.S. Pat. Nos. 4,427,500 and 4,581,996 both corresponding to JP-B-3-42196 (the term xe2x80x9cJP-Bxe2x80x9d as used herein means an xe2x80x9cexamined Japanese patent publicationxe2x80x9d) specify the shape of a roughened surface obtained by preliminarily graining of a base material to a center line average roughness of up to 0.1 xcexcm.
The above-mentioned inventions are excellent inventions. However, printing plates of higher quality have been desired from recent customers"" needs, and the development of supports for lithographic printing plates fitting the needs have been desired. Further, it is necessary to decrease the production cost to a maximum.
In JP-A-6-92052 and JP-A-6-24166, no preliminary graining is conducted, so that the surface roughness after rolling is rough. When mechanical surface roughening, chemical etching and electrochemical surface roughening are applied to original aluminum having projecting streaks, photosensitive layers on projections become thin in sections of projecting streaks or in sections whose roughness is rough after coating, resulting in the development of disadvantages such as a reduction in printing durability and poor appearance at the sections. Further, JP-B-3-42196 discloses that the base material is preliminarily polished to a center line average roughness of up to-0.1 xcexcm. However, in order to carry out this, much labor and cost are required, and the production cost is sometimes increased very high.
An object of the present invention is to provide lithographic printing plates having improved printing performance, increased efficiency of exposure and development procedures, improved flatness of the lithographic printing plates, and improved productivity of the lithographic printing plates.
Another object of the present invention is to provide a method for producing a support for a lithographic printing plate, which solves the above-mentioned problems, gives uniform quality and minimizes the production cost.
Intensive investigations and studies of the present inventors for solving the above-mentioned problems has resulted in completion of the present invention.
That is, the present invention provides (1) a lithographic printing plate having an average curvature in a rolling direction of 1.5xc3x9710xe2x88x923 mmxe2x88x921 or less, a curvature distribution in a crosswise direction of 1.5xc3x9710xe2x88x923 mmxe2x88x921 or less, and a curvature in a direction perpendicular to said rolling direction of 1.0xc3x9710xe2x88x923 mmxe2x88x921 or less.
The present invention further provides (2) a lithographic printing plate having an average surface roughness of 0.3 to 0.8 xcexcm, a difference between an average surface roughness in a rolling direction and that in a direction perpendicular to the rolling direction of 30% or less of said average surface roughness, and further having an average curvature in a rolling direction of 1.5xc3x9710xe2x88x923 mmxe2x88x921 or less, a curvature distribution in a crosswise direction of 1.5xc3x9710xe2x88x923 mmxe2x88x921 or less, and a curvature in a direction perpendicular to said rolling direction of 1.0xc3x9710xe2x88x923 mmxe2x88x921 or less.
The present invention still further provides (3) a method for producing the lithographic printing plate described in (1) or (2) described above, which comprises performing a surface roughening treatment and an anodic oxide coating treatment on an aluminum plate, coating a photosensitive layer thereon, and then correcting said aluminum plate by use of correcting rolls having a diameter of 20 mm to 80 mm and a rubber hardness of 50 to 95 degrees.
The present invention further provides (4) a method for producing a support for a lithographic printing plate comprising roughening a surface of an aluminum base material having a center line average surface roughness of 0.15 to 0.35 xcexcm and a maximum surface roughness of 1 to 3.5 xcexcm by at least one of mechanical surface roughening, chemical etching and electrochemical surface roughening, and then applying anodization thereto.
It is preferred that the center line average surface roughness and the maximum surface roughness of said aluminum base material are given by preliminary graining, said preliminary graining being conducted by direct current electrolytic graining or by use of a roll formed of nonwoven fabric containing an abrasive with a mean grain size of 1 to 25 xcexcm.